The present disclosure relates to solid oxide fuel cells, and more particularly relates to a solid oxide fuel cell structure including a fluid distribution system.
Alternative transportation fuels have been represented as enablers to reduce toxic emissions in comparison to those generated by conventional fuels. At the same time, tighter emission standards and significant innovation in catalyst formulations and engine controls have led to dramatic improvements in the low emission performance and robustness of gasoline and diesel engine systems. This has certainly reduced the environmental differential between optimized conventional and alternative fuel vehicle systems. However, many technical challenges remain to make the conventionally fueled internal combustion engine a nearly zero emission system having the efficiency necessary to make the vehicle commercially viable.
Alternative fuels cover a wide spectrum of potential environmental benefits, ranging from incremental toxic and carbon dioxide (CO2) emission improvements (reformulated gasoline, alcohols, liquid petroleum gas, etc.) to significant toxic and CO2 emission improvements (natural gas, dimethylether, etc.). Hydrogen is clearly the ultimate environmental fuel, with potential as a nearly emission free internal combustion engine fuel (including CO2 if it comes from a non-fossil source). Unfortunately, the market-based economics of alternative fuels, or new power train systems, are uncertain in the short to mid-term.
The automotive industry has made very significant progress in reducing automotive emissions in both the mandated test procedures and the xe2x80x9creal worldxe2x80x9d. This has resulted in some added cost and complexity of engine management systems, yet those costs are offset by other advantages of computer controls: increased power density, fuel efficiency, drivability, reliability and real-time diagnostics.
Future initiatives to require zero emission vehicles appear to be taking us into a new regulatory paradigm where asymptotically smaller environmental benefits come at a very large incremental cost. Yet, even an xe2x80x9cultra low emissionxe2x80x9d certified vehicle can emit high emissions in limited extreme ambient and operating conditions or with failed or degraded components.
One approach to addressing the issue of emissions is the employment of fuel cells, particularly solid oxide fuel cells (xe2x80x9cSOFCxe2x80x9d), in an automobile. A fuel cell is an energy conversion device that generates electricity and heat by electrochemically combining a gaseous fuel, such as hydrogen, carbon monoxide, or a hydrocarbon, and an oxidant, such as air or oxygen, across an ion-conducting electrolyte. The fuel cell converts chemical energy into electrical energy. A fuel cell generally consists of two electrodes positioned on opposites of an electrolyte. The oxidant passes over the oxygen electrode (cathode) while the fuel passes over the fuel electrode (anode), generating electricity, water, and heat.
SOFC""s are constructed entirely of solid-state materials, utilizing an ion conductive oxide ceramic as the electrolyte. A conventional electrochemical cell in a SOFC is comprised of an anode and a cathode with an electrolyte disposed therebetween. In a typical SOFC, a fuel flows to the anode where it is oxidized by oxygen ions from the electrolyte, producing electrons that are released to the external circuit, and mostly water and carbon dioxide are removed in the fuel flow stream. At the cathode, the oxidant accepts electrons from the external circuit to form oxygen ions. The oxygen ions migrate across the electrolyte to the anode. The flow of electrons through the external circuit provides for consumable or storable electricity. However, each individual electrochemical cell generates a relatively small voltage. Higher voltages are attained by electrically connecting a plurality of electrochemical cells in series to form a stack.
The SOFC cell stack also includes conduits or manifolds to allow passage of the fuel and oxidant into and byproducts, as well as excess fuel and oxidant, out of the stack. Generally, in certain cell configurations, oxidant is fed to the structure from a manifold located on one side of the stack, while fuel is provided from a manifold located on an adjacent side of the stack. The fuel and oxidant are generally pumped through the manifolds. From the manifolds, the fuel and oxidant are separately introduced to fluid distribution surfaces on an appropriate structure such as an interconnect between cells or an end cap. The fluid distribution surfaces are positioned in fluid communication with the appropriate electrode, with the SOFC efficiency related, in part, to fluid distribution across the surface of the electrode.
Typically, fuel is introduced at the edge of the interconnect reacts with the electrode. The reaction (at an anode) generally creates electrons and water, wherein the water mixes with the fuel flowing across the electrode. Therefore, certain regions of the electrode are prone to diminished current density, since the fuel used at certain regions contains spent fluid, thus a decreased concentration in fuel.
What is needed in the art is an enhanced structure for distributing fluid to electrodes of SOFC""s, particularly for distributing fresh fuel to anodes of SOFC""s.
The drawbacks and disadvantages of the prior art are overcome by an electrode fluid distributor includes a fluid passageway having a plurality of adjacent pairs of segments each including an inlet segment in fluid communication with an inlet and an outlet segment in fluid communication with an outlet. A baffle is disposed between adjacent inlet and outlet segments. Each inlet segment is in fluid communication with adjacent inlet segments and adjacent outlet segments, and each outlet segment is in fluid communication with adjacent outlet segments.